This application claims the priority of Korean Patent Application No: 2003-9097, filed on Feb. 13, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a molecular sieve and more particularly, to a carbon molecular sieve. The present invention also relates to a fuel cell and more particularly, to a catalyst and a catalyst support for a fuel cell.
2. Description of the Related Art
Originally, the term xe2x80x9cmolecular sievexe2x80x9d was the trade name of a synthetic zeolite commercially manufactured by Linde Ltd. (USA). A molecular sieve has excellent adsorption capacity due to its many fine pores with uniform diameter. As derived from its literal meaning, a molecular sieve is used to selectively sieve molecules.
Presently, the term xe2x80x9cmolecular sievexe2x80x9d is an generic name in the field of science technology and refers to a porous material in which uniform-sized pores are arranged in a three dimensional manner.
A molecular sieve selectively adsorbs a certain size of molecules due to its uniform pore size. Therefore, a molecular sieve can be widely used as a catalyst, a catalyst support, or an adsorbent.
A carbon molecular sieve is mainly made of a carbon material. A carbon molecular sieve has many advantages, such as excellent thermal stability, hydrothermal stability, chemical resistance, and lipophilicity, when compared to a metal oxide based molecular sieve such as zeolite. A carbon molecular sieve can also be used for various purposes, such as a catalyst support, an adsorbent, a sensor, and an electrode material.
As one example of a method for synthesis of a carbon molecular sieve, there is disclosed a pyrolysis process of a natural vegetable material, such as coconut, or a synthetic polymer. According to this method, however, pore size and porosity can only be limitedly increased by pyrolysis temperature adjustment and post-treatment with oxygen.
Another example of a method for synthesis of a carbon molecular sieve is disclosed in Korean Patent Application Laid-Open Publication Nos. 2001-1127 and 2002-84372. According to these methods, a mesoporous silica molecular sieve is used as a template. A carbohydrate is subjected to adsorption into the template, polymerization and pyrolysis. The template is then removed to thereby produce a carbon molecular sieve with a structural regularity of uniform-sized pores. However, a disadvantage exists in that a silica molecular sieve used as a template must be newly designed to adjust the surface area of the carbon molecular sieve and the volume ratio of its micropores and mesopores. In addition, it is difficult to control the volume ratio between micropores and mesopores.
Fuel cells are clean energy sources capable of reducing dependence on fossil energy, with a high output density and high energy conversion efficiency. In addition, fuel cells can be operated at room temperature and can be miniaturized and packed. Therefore, fuel cells can be widely used in the fields of zero emission vehicles, domestic power systems, mobile communication equipment, medical instruments, military equipment aerospace equipment, and portable electronic devices. A polymer electrolyte membrane fuel cell (PEMFC) and a direct methanol fuel cell (DMFC) are electric power generating systems that allow electrochemical reaction of hydrogen or methanol, water, and oxygen to produce direct current electricity. These fuel cells comprise an anode and a cathode which receive a liquid/gaseous reactant and a proton conducting membrane interposed between the two electrodes. At the anode, an anode catalyst dissociates hydrogen or methanol to generate protons. The generated protons are transported through the proton conducting membrane to the cathode. At the cathode, the protons react with oxygen by the cathode catalyst. Therefore, in such structured fuel cells, the role of a catalyst is very important. Currently, in a PEMFC, platinum (Pt) particles supported on a carbon support are used as both anode and cathode catalysts. In DMFCs, platinum-ruthenium (Ptxe2x80x94Ru) black is used as an anode catalyst and Pt particles by themselves or Pt particles supported on a carbon support are used as a cathode catalyst. Because metal black by themselves provide excellent catalytic activity, a supported metal catalyst system is rarely used in a DMFC. However, because a large portion of costs incurred in a DMFC is caused by a catalyst, in considering cost effectiveness, the amount of a used catalyst needs to be decreased. Therefore, many efforts have been made to research a carbon support capable of providing improved catalyst activity and dispersion over a currently used carbon support with no structural regularity, in order to reduce the catalyst amount used in an anode and a cathode.
The present invention provides a method for manufacturing a carbon molecular sieve with increased microporosity.
The present invention also provides a method for manufacturing a carbon molecular sieve with increased microporosity and improved structural regularity.
The present invention also provides a carbon molecular sieve with increased microporosity.
The present invention also provides a carbon molecular sieve with increased microporosity and improved structural regularity.
The present invention also provides a catalyst for a fuel cell containing the aforementioned carbon molecular sieve.
The present invention also provides a fuel cell employing the aforementioned catalyst.
According to an aspect of the present Invention, there is provided a method for manufacturing a carbon molecular sieve, comprising the steps of (a) impregnating pores of a mesoporous silica molecular sieve, used as a template, with a mixture of a silica oligomer, a condensable or polymerizable carbon-containing compound, used as a carbon precursor, and a liquid carrier; (b) polymerizing the carbon precursor to form a carbon precursor polymer within the pores of the template; (c) carbonizing the carbon precursor polymer using pyrolysis; and (d) removing the template and the silica oligomer using a solution capable of dissolving silica selectively.
According to another aspect of the present invention, there is provided a method for manufacturing a carbon molecular sieve, comprising the steps of (a) impregnating micropores of an ordered mesoporous silica molecular sieve, used as a template, having the mesopores and the micropores that are responsible for the connections between the mesopores, with a first mixture comprising a condensable or polymerizable carbon-containing compound, used as a carbon precursor, and a liquid carrier; (b) polymerizing the carbon precursor within the micropores of the template to form a carbon precursor polymer within the micropores of the template; (c) impregnating the mesopores of the template with a second mixture comprising a silica oligomer, a condensable or polymerizable carbon-containing compound, used as a carbon precursor, and a liquid carrier; (d) polymerizing the carbon precursor within the mesopores of the template to form a carbon precursor polymer within the mesopores of the template; (e) carbonizing the carbon precursor polymers within the template using pyrolysis; and (f) removing the template and the silica oligomer using a solution capable of dissolving silica selectvely.
According to another aspect of the present invention, there is provided a carbon molecular sieve having mesopores and micropores. The total volume of pores, with a size of 80 nm or less, is 1.0 cm3/g or more and microporosity is 35% or more.
According to another aspect of the present invention, there is provided a catalyst for a fuel cell comprising a porous catalyst support and catalytic metals dispersed on the catalyst support, wherein the catalyst support is the aforementioned carbon molecular sieve.
According to yet another aspect of the present invention, there is provided a fuel cell using the aforementioned catalyst.